1. Field of the Invention
The present invention relates to a Label Switching Router (hereinafter abbreviated as LSR), and in particular to a label switching router placed at an end of an LSP (Label Switched Path).
2. Description of the Related Art
FIG. 28 shows a state in which a prior art router performs a packet transfer process by a software processing in the layer 3 by referring to a destination address. An IP packet P1 transmitted from an entrance router 1 reaches an exit router 3 through a middle router 2.
On the other hand, FIG. 29 shows a packet transfer process by LSR's 1-3 which are routers used for MPLS (Multi Protocol Label Switching). The MPLS allocates 20 bits label to an IP communication traffic designated by an FEC (Forwarding Equivalence Class), thereby enabling switching by a hardware processing by a fixed length label (Shim header) in the layer 2.5. The MPLS is a technology for transferring a packet at a high speed.
As shown in FIG. 29, a label “a” is attached to an IP packet P1 at an entrance LSR 1, so that the IP packet P1 is transmitted to a middle LSR 2. At the middle LSR 2, the label “a” of the IP packet P1 is replaced with a label “b”, so that the IP packet P1 is transmitted to an exit LSR 3. In this case, the label “a” assumes an incoming label, and the label “b” assumes an outgoing label at the middle LSR 2. At the exit LSR 3, the label “b” is deleted, thereby obtaining the original IP packet P1.
Also, FIG. 30 shows an arrangement of a general LSR, in which an LSR 100 is composed of line interfaces 101 and 106, a CPU 102, a switch 103, an LSI 104 for retrieval, a memory 105, and a memory 107 for a retrieval table. The LSR's 1-3 in FIG. 29 have the same arrangement.
The CPU 102 in the LSR 100 realizes an MPLS function by using various data held in the memory 105.
In operation, the frame (e.g. label “a” is attached as incoming label) received from the line through the line interface 101 is sent to the switch 103. The switch 103 inquires of the retrieving LSI 104 the outgoing label corresponding to the incoming label. The retrieving LSI 104 determines the outgoing label (e.g. label “b”) referring to the retrieval table set by the CPU 102 and held in the memory 107 for the retrieval table.
The switch 103 transmits the frame, to which the label “b” notified from the retrieving LSI 104 is attached as an outgoing label, to the line through the line interface 106.
It is necessary that the correspondence between the incoming label and the outgoing label is preset and the LSP is set up (established) in order that the LSR performs the above-mentioned operation. Such an LSP setup process will now be described referring to FIG. 31.
In FIG. 31, the LSR 100 connected to a communication line 70 is composed of an MPLS processor 60, a label manager 50, and a switch setting portion 40. An LSP setup accepting portion 10, a message transmitter 20, and a message receiver 30 are provided in the MPLS processor 60.
It is assumed that an LSR 200 whose arrangement is the same as that of the LSR 100 is connected to the end of the communication line 70, and the LSP is to be set up between the LSR's 100 and 200.
When accepting an external LSP setup request S1 at the LSP setup accepting portion 10, the MPLS processor 60 of the LSR 100 performs a label request message transmission S3 to the communication line 70 from the message transmitter 20 by instructions S2 of the LSP setup accepting portion 10.
At the LSR 200 on the message reception side, its own message receiver 30 performs a label request message reception S4 from the communication line 70. The MPLS processor 60 performs a label request S5 from the label manager 50, and receives a notification S5 of a label to be allocated by the label manager 50. The label is notified to the LSR 100 which is the source of the label request message by a label mapping message at the message transmitter 20.
At the source LSR 100 which has received the label notification in the label mapping message, the MPLS processor 60 performs a label setting S6 to the switch setting portion 40.
The MPLS automatically establishes a best effort type LSP by cooperating with the existing routing protocol. The LSP is a unidirectional path, so that two independent LSP's are required to perform a bidirectional communication.
However, in the prior art MPLS, only a single unidirectional LSP can be set with a single operation. Therefore, in order to perform the bidirectional communication between the apparatuses, it is necessary for a management person to perform the LSP setup at two LSP's which assume the entrances of each LSP respectively, or for an external database server which grasps the entire network to request the LSP setup from the two LSR's which assume the entrances of each LSP, resulting in problems as follows:    (1) In case the LSP setup operation is performed at the two LSR's which assume the entrances, it is necessary to perform an up direction LSP setup and a down direction LSP setup respectively. Since it takes time to establish a bidirectional LSP, a real-time operation can not be performed.    (2) In case the external database server is used, a database amount swells in proportion to the network scale, so that a memory amount and the load of the server increase. Since it is required that information is notified from each LSR to the server, the load of the network also increases. Furthermore, it takes more time to prepare the database as the network scale becomes larger, so that a real-time operation for starting the bidirectional communication is missed.
As a solution for such problems, a bidirectional LSP setup method has been proposed in the “packet relaying apparatus” of the Japanese Patent Application Laid-open No.11-150634 (hereinafter, referred to as a PAA apparatus) by the applicant of the present invention.
This method is characterized in that an available range and a directionality (direction) of a label are determined by a negotiation with an adjoining packet relaying apparatus, a label distribution protocol processor for allocating the label to a forwarding equivalence class treats a unidirectional forwarding equivalence class and another forwarding equivalence class opposite in direction to the former forwarding equivalence class as a single bidirectional forwarding equivalence class, and allocates the label to the bidirectional forwarding equivalence class.
FIG. 32 shows a simultaneous allocation example of the same label between ATM-LSR_A and ATM-LSR_B which are adjoining LSR's in the PAA apparatus (partially omitted).
Firstly, the ATM-LSR_A includes information indicating that a symmetrical FEC can be simultaneously allocated in a label request message S31 transmitted to the ATM-LSR_B. The ATM-LSR_B includes a label allocated to the ATM-LSR_A and information indicating that the simultaneous allocation of the symmetrical FEC has been performed in a label mapping message S32 transmitted to the ATM-LSR_A.
Thus, it becomes possible to set up a pair of bidirectional LSP's with a single operation by the ATM-LSR_A.
However, since the PAA apparatus is characterized by the label allocation method of the adjoining packet relaying apparatuses, it is necessary for all of the LSR's existing on the route of the LSP to be provided with such a label allocation function.
On the other hand, apart from the above-mentioned problems (1) and (2), the necessity of a quality of service guarantee (hereinafter, occasionally abbreviated as QoS guarantee) in the IP communication network has been rapidly increasing recently by the appearance of VOIP (Voice Over IP) and RTP (Real-time Transport Protocol).
As a technology for providing the QoS guarantee for the MPLS, CRLDP (Constraint-based Routing Label Distribution Protocol) which is the label distribution protocol treating a constraint route is known. It is possible to designate the QoS guarantee and the LSP path and to statically set the LSP with the CRLDP.
The designation of the QoS guarantee and the LSP path (explicit route) in the CRLDP is realized by setting a traffic parameters TLV and an explicit route parameters TLV in the label request message transmitted when the label switching router placed at one end of the LSP requests the LSP setup from the label switching router at the other end.
Although the necessity of the bidirectional communication having the QoS guarantee is further increasing in the MPLS according to the development of the Internet and the arrangement of the social infrastructure, the solution of the QoS guarantee issue has been attempted by using the CRLDP.
In the present IP communication network, the communication between the server and the client such as a VOIP communication, a file transfer, and the Web browsing occupies the most part of the IP traffic, so that in such a communication the bidirectional communication is always required.
However, in order to apply the PAA apparatus for the matter of the bidirectional communication, it is necessary that all of the relaying apparatuses within the network are replaced with ones having the function of the PAA apparatus, so that the introducing cost steeply rises especially in case of a large-scale network.